1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device and a method for fabricating the same using a liquid crystal dispensing method and a bonding apparatus for bonding substrates at an atmospheric pressure.
2. Discussion of the Related Art
Demands for display devices have increased with development of an information society. Accordingly, many efforts have been made to research and develop various flat display devices, such as liquid crystal display (LCD) devices, plasma display panel (PDP) devices, electro-luminescent display (ELD) devices, and vacuum fluorescent display (VFD) devices. In particular, liquid crystal display (LCD) devices have been most widely used as a substitute for a cathode ray tube (CRT) because of their advantageous characteristics of thin profile, lightness, and low power consumption. LCD devices have been implemented as display devices for notebook computers, desktop computers, televisions, and the like. One consideration in developing LCD devices is to develop LCD devices having a high quality picture, such as high resolution and high luminance with a large-sized screen, while maintaining lightness, thin profile, and low power consumption.
In general, the LCD device includes an LCD panel for displaying an image and a driver for supplying a driving signal to the LCD panel. In addition, the LCD panel includes first and second substrates attached to each other with a cell gap therebetween, and a liquid crystal layer formed in the cell gap. Further, alignment layers are respectively formed on facing surfaces of the first and second substrates, wherein the alignment layers are rubbed to align the liquid crystal layer. For maintaining fixed cell gaps between the first and second substrates, spacers are spread or fixed between the first and second substrates.
The first substrate or a thin film transistor array substrate includes a plurality of gate lines arranged along a first direction, a plurality of data lines arranged along a second direction perpendicular to the first direction, a plurality of pixel electrodes arranged in a matrix-type configuration within pixel regions defined by the crossings of the gate and data lines, and a plurality of thin film transistors for switching signals from the data lines to the pixel electrodes based on signals received from the gate lines.
Further, the second substrate or a color filter array substrate includes a black matrix layer, a color filter layer, and a common electrode. The color filter layer includes red, green, and blue color filters, wherein the color filter layer is formed by repetitively positioning the color filters in order of red(R), green(G), and blue(B) within regions corresponding to the pixel regions of the first substrate. Alternatively, in a liquid crystal display device of an In Plane Switching (IPS) mode, the common electrode may be formed on the first substrate. Accordingly, the liquid crystal layer controls the intensity of light, and the light passes through the color filter layers of red(R), green(G), and blue(B) to represent color images.
In particular, the liquid crystal display layer is formed by a liquid crystal injection method or a liquid crystal dispensing method. In a liquid crystal injection method, two substrates are bonded to each other with an liquid crystal injection hole formed in the seal pattern, and a liquid crystal material is injected between the two substrates via the liquid crystal injection hole. In a liquid crystal dispensing method, an appropriate amount of the liquid crystal material is dispensed on one of the two substrates, and the two substrates are bonded to each other.
FIG. 1 illustrates a system for bonding substrates using a liquid crystal injection method according to the related art. As shown in FIG. 1, the two bonded substrates 10 are placed into a vacuum chamber 20 having a container 30 holding a liquid crystal material 31 therein. Then, a vacuum pump 25 evacuates the vacuum chamber 20, and the liquid crystal injection hole (not shown) in the bonded substrates 10 contacts the liquid crystal material 31 held in the container 30. Further, air or N2 gas is supplied to the vacuum chamber 20 to bring the vacuum chamber 20 into an atmospheric pressure state. As a result, the liquid crystal material 31 is injected between the two bonded substrates 10 by the capillary tube phenomenon. When the liquid crystal material 31 is filled between the two bonded substrates fully, the liquid crystal injection hole is sealed.
FIG. 2 illustrates a system for bonding substrates using a liquid crystal dispensing method according to the related art. As shown in FIG. 2, a substrate bonding apparatus is placed inside a vacuum chamber 21. The substrate bonding apparatus includes an upper stage 40 for holding a first substrate 10a, a lower stage 41 for holding a second substrate 10b having the liquid crystal material 31 dispensed thereon, a vacuum pump 25 for evacuating the vacuum chamber 21, and a vent means 26 for injecting gas or air into the vacuum chamber 21. Although not shown, the upper, and lower stages 40 and 41 are provided with vacuum holes, and electrostatic chucks for adsorbing and holding the substrates 10a and 10b, respectively.
In addition, a seal pattern 27 is formed on a periphery of the second substrate 10b, and the liquid crystal material 30 is dispensed inside the seal pattern 27. Although not shown, column spacers are formed on one of the first and second substrates 10a and 10b, and an alignment film also is formed on one of the first and second substrates 10a and 10b. 
In particular, the first substrate 10a having no liquid crystal material dispensed thereon is loaded on the vacuum chamber 21, and the upper stage 40 is moved down under the control of a moving means 42 to adsorb the first substrate 10a. Then, the second substrate 10b having the liquid crystal material 30 dispensed thereon is loaded on the vacuum chamber 21 and positioned on the lower stage 41, so that the lower stage 41 adsorbs the second substrate 10b by vacuum.
Then, the upper and lower stages 40 and 41 respectively hold the first and second substrates 10a and 10b using the electrostatic chucks for preventing the substrates 10a and 10b from falling off the respective stages 40 and 41 at the time of evacuation of the vacuum chamber 21.
After securing the first and second substrates 10a and 10b with the upper and lower stages 40 and 41, the vacuum pump 25 is turned on to evacuate the vacuum chamber 21. Then, the upper stage 40 is moved down to bond the first and second substrates 10a and 10b with the seal pattern, and air or gas is injected through the vent means 26 to bring the vacuum chamber 21 into an atmospheric state. Then, because an inside of the two bonded substrates is in a vacuum state and the vacuum chamber 21 is in the atmospheric state, the two substrates are pressed and bonded by a pressure difference.
In particular, the bonding of the first and second substrates 10a and 10b are performed in a vacuum state for increasing fluidity of the dispensed liquid crystal material 31 to uniformly distribute the liquid crystal material. If the distribution of the liquid crystal material 31 is not uniform, bubbles may be formed in the resultant liquid crystal layer, thereby causing defects, such as picture distortion in the resultant liquid crystal display panel.
In addition, the apparatus and method for fabricating a liquid crystal display device according to the related art have the following problems. First, the related art liquid crystal injection method requires the vacuum chamber, the vacuum pump, and the like for injection of the liquid crystals in a vacuum state, thereby requiring complex system and increasing production cost. Further, the liquid crystal dispensing method according to the related art also requires the vacuum chamber, the vacuum pump, the electrostatic chucks, and the vent means to perform bonding of the first and second substrates in a vacuum state, thereby increasing production cost. Moreover, since the vacuum chamber needs to be evacuated, overall production time is prolonged, thereby reducing fabrication efficiency.
Furthermore, in the related art, smooth spread of the liquid crystals is achieved by creating a pressure state for the dispensed liquid crystals at a vacuum. However, to create the environment for the liquid crystals at a vacuum is complicate since vacuum suction is not applicable to the holding of the substrates at the stages due to the vacuum state of an inside of the vacuum chamber.